Automatic telephone system



Oct. 26, 1926.

J. WICKS AUTOMATIC TELEPHONE SYSTEM 4 Sheets-Sht 1 original Filed June 17. 1920 Oct. 26 1926. 1,604,372

J. WICKS AUTOMATIC TELEPHONE SYSTEM original Filed June 17. 1920 4 sh t -s t 2 REEF 1H3? AUTOMATI C TELEPHONE SYSTEM LISTEN Ol /e5 HEAD 5E7" Oct. 26 1926.

J. WICKS .AUTOMATIC TELEPHONE SYSTEM Original Filed June 1'7. 1920 4 Sheets-Shec. L

Patented Oct. 26, 1926.

UNITED STATES PATENT OFFICE.

JOHN'WICKS, OF OAK PARK, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC INC, OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE.

nuromarro TELEPHONE sYs'rEM.

Application filed June 17, 1920, Serial No. 389,633. Renewed January 2, 1926.

My invention relates in general to automatic telephone systems, but appertains more especially to such systems as include in addition tothe regular local trunking system a second trunking system commonly known as a toll service trunking system, which is used for the interconnecting of toll or long distance lines with local lines; and the object of the invention is the provision of circuit arrangements constituting essentially a third trunking system accessible to switches in both of the above systems and provided for the useof local subscribers and toll operators in calling automatic private branch exchanges.

The use of an attendants cabinet at each private branch exchange, with the inevitable complications, and the desirability of pro- 1 viding for absolutely uniform routine operations on the part of toll operators regardless of whether they are calling main exchange or private branch exchange lines, give rise to numerous problems "of exceptional difficulty, which have been solved by an entire redesign of the main to branch exchange trunk circuits. The new features introduced andtheir relation to the system as a whole will be fully explained hereinafter, reference being had to the accompanying drawings.

The invention resides entirely in i the branch exchange trunking system, and in Figs. 1, 2, 3, and 4 I have shown by means of the usual circuit diagrams all the apparatus in a trunking system of the above character which is required to complete a connection from the main exchange to a local line in a private branch exchange. Fig. 5 shows the wiring of the test contacts in a branch exchange connector, and Fig. 6 is a schematic diagram illustrating the general layout of the system.

Referring to the latter figure, the schematic diagram, this is intended to show the relation of the three trunking systems to each other and the manner in which they are blended together to form a complete telephone exchange system. The exchange may of course be of any desired capacity. How-.

ever, for convenience it will be assumed to' have a capacity of 10,000 lines, that is, connections are established by means of first selectors. second selectors, and connectors of the usual Strowger/verticaland rotary. type. Thus the; subscriber at substation A can extend a connection to the line of substation A by means of the individual line switch C, the first selector D, the second selector F, and the connector H. This is the usual decimal trunking system and is used for com pleting local calls in the main exchange.

Toll connections are completed by means .of a toll service trunking system, as before stated. For example, a toll'operator can extend a connection to the line of substation A by means of ack J, toll first selector D toll transmission repeater E toll second selector F and the connector H. It will be noticed that the connector H is included in both trunking systems, and it appears then that the local trunking system and the toll service trunking system are merged or blended-together at the connectors. The connector II is known as a combination toll and regular connector, and it should be stated that the layout as explained so far,

including these combination connectors, is old and is fully described in my U. S. Patent #1,?315A44, granted Sept. 2, 1919. The exact circuits used in the toll service trunking system, however, are preferably of the improved typev shown in my copending appli2c0ation, Serial No. 379,217, filed May 6,

We 'now come to the private branch exchange trunking system, which is the subject matter of the invention. In order to handle calls to the branch exchanges a group of special second selectors, or selector repeaters, as they may be termed, is provided which are accessible to'local subscribers and also to tell operators by way 'of a certain designated level at the first selectors. In other words, the trunk lines from a certain level in the local first selectors and the trunk lines from the corresponding level in the toll first selectors extend to the .same grou of second selectors, which are the specia see lectors referred to. This means that there are two trunk lines whichextend to each special selector and the trunk lines of each pair are merged or combined into one trunk line at a special switching mechanism or so called combination regular and toll transmission repeater which is interposed ahead of the special selector to which the single trunk line thus formed is extended. "The main to branch exchange trunk lines serving a branch exchange are accessible to the. special-second selectors and extend to the branch exchange where after passing through the attendant operators position or cabinet they terminate in connectors which have access to the local lines in the branch exchange.

With this explanation, a call may now be traced'from the main exchange to the branch exchange. For example, the subscriber at substation A can extend a connection to the line of branch substation A by means of individual line switch C, first selector D, combination regular and toll transmission repeater E, special second selector F, and connector H. Also a toll connection to the same branch substation may be completed by way of jack J, toll first selector D combination regular and tell transmission repeater E, special second selector F, and connector H. It will be observed that the route followed after the calls get past the first selectors is the same in both cases.

The circuit drawings show only apparatus which is included in the branch exchange trunking system, and which comprises the combination regular and toll transmission repeater E, shown in Fig. 1, the special second selector F, Fig. 2, and a main to branch exchange trunk line which is accessible to the special selector F and extends by way of the attendant operators cabinet, Fig. 3, to the connector H, Fig. 4. It should be mentioned that the trunk line shown is a two way trunk line, that is, it may be used not only for connections from the main exchange to the branch "exchange, but also for interchange connections which are originated in the branch exchange. This however, is more or less of an incidental feature and on that account is not indicated in the schematic drawing, Fig. 6, but is shown in the circuit diagrams and will be explained in the detailed specification. To avoid confusion it may also be stated at this time that the combination regular and toll repeater E is not, strictly speaking, a repeater, at least not an impulse repeater, for it does not repeat impulses, this function being performed by the line relay of the adjacent selector F. The location of this line relay is, however, a mere matter of convenience and since the repeater E performs all the other functions of arepeater of this type, and since it is, furthermore, conveniently known and referred to as such from its position in the trunking system, it will be termed a repeater herein.

Main to branch emchahge connection.

Having indicated in general terms the purpose and scope of the invention, I will now describe in a more detailed manner the operation of the circuits when used for setting up a connection. For thispurpose it will be assumed that a calling subscriber in the main exchange, as for example, the sub scriber at substation A, Fig.6, desires to obtain connection with a called subscriber at the branch exchange, as for example, the subscriber at substation A. The general method of setting up the connection and the apparatus involved have already been de: scribed briefly and the operation of the apparatus shown'in the circuit drawings will now be pointed out in detail.

WVhen the receiver is removed at substation A the individual line switch C is operated and the calling line is extended by means of the line switch to an idle first selector switch which we will assume to be the selector D, Fig. 6. The calling subscriber will now operate his calling device in accordance with the first digit in the desired number. Since the Wanted party is in a private branch exchange the first digit in the number will correspond to the selector level which is reserved for the branch exchange trunking system, and when the calling device is operated in accordance with this digit the selector D will be operated to raise its wipers to this level, after which the automatic trunk selecting movement is initiated as usual and the wipers are rotated automatically to select an idle trunk line.

referring now to Fig. 1, the trunk line con1- prising conductors 8, 9 and 10 is one of the trunk lines to which the selector D has access by way of the branch exchange level and this trunk line extends from the multi- :ple bank contacts 2, 3 and 4:, located in the bank of the selector D and Inultipledto similar contacts in the banks of other selectors, to the combination regular and toll transmission repeater E. Assuming ,now that the above trunk line is the one selected, when the wipers of the selector D establish connection with the bank contacts 2, 3, and 4, the calling subscribers line will be extended by way of the selector line wipers, bank contacts 2 and 4, conductors 8 and 10, upper and lower left hand windings of the repeating coil R, conductors 76 and 71, normally closed contact springs of the reversing relay 18, conductors 72 and 73, normally closed contacts of relay 24, conductors 62 and 63, and the upper and lower windings of the double wound line relay 101 of the selector F, Fig. 2, to battery and ground respectively.

When the calling line is extended as above the line relav 101 is energized by current flow through the calling substation and upon attracting its armature, closes a circuit for the slow acting release relay 102.

Upon energizing, relay 102 prepares the selector F for operation in its vertical movement in the usual manner, and also places a ground upon the release trunk conductor 9. By this latter operation a ground potential is placed upon the test contact 3 and'its multiples in the banks of the selector switches having access to the trunk line, and

. tact 6 and its multiples, which are located in the banks of the toll first selectors having access to the trunk line comprising conductors 11, 12, and 13, are brought near enough times,

to ground potential by the above connection to make the trunk line busy. The grounding of conductor 9 also produces cer tainresults in the repeater E which are now to be pointed out. When this conductor is grounded current flows over a branch which extends from junction point by way of the resistance 74 and the upper winding of the electropolarized relay 15 to battery. Resistance 74 is very high, preferably about 8000 ohms, and the relay 15 accordingly is not operated. Another branch circuit which may be traced extends from junction point 7 5 by way of armature 25 and its resting contact, conductor 76, and through the windings of relays 20 and 21 in parallel to battery, the circuit through the latter relay including the armature 48 of relay 22. Relays 20 and 21 are accordingly energized and produce various circuit changes which, however, are of no eflect just at the present time. It may be noted, however, that relay 21 is the ring out ofi relay and upon energizing, this relay disconnects the ringing equipment .at the resting contacts of 'its armatures 43 and 46, and at the working contacts'of these armatures extends the right hand windings of the repeating coil R through to the outgoing trunk conductors 60 and 64.

The calling subscriber may now operate his calling device in accordance with the next digit in the called number. .As a result a series of interruptions is produced in the line circuit and the line relay 101 of the selector F is deenergized a plurality of transmitting at each deenergization an impulse of current through the slow acting relay 103 and the vertical magnet 107 in series to battery. In response to these impulses the vertical magnet is operated to raise the wipers 130, 131, and 132 until they stand opposite the level of bank contacts which is assigned to the trunk lines extending to the particular branch'exchange in which the wanted line is located. The slow acting relay 103 is energizedin series with the vertical magnet and retains its armature in'operated pos1tion throughout the vertical movement ward step of the shaft the 011? normal springs of the switch. At the first upare shifted and relay 103 being new in operated position a circuit is completed from the grounded conductor 9 by way of the armature of relay 103, the oil normal springs 114, and the winding of the stepping relay 104 to battery. Relay 104 is therefore energized, establishes a locking circuit for itself at its lower armature, and at its upper armature prepares a circuit for the rotary magnet .105. Upon the cessation of the impulses to. the vertical magnet the slow acting relay 103 falls back and closes the circuit of the rotary magnet 105, which is energized and operates to rotate the switch wipers into engagement with the first set of contacts in the level opposite which they were raised.

Near the end of-its stroke the rotary magnet I breaks the locking circuit of the stepping relay 104 which deenergizes and breaks the circuit of the rotary magnet. The rotary magnet then deenergizes also and again closes its interrupter contact. The operation now depends upon whether the trunk line terminating in the first set of bank contacts is busy or idle. If this trunk line is busy the test contact with which the test wiper 131 is in engagement will have a ground potential upon it and a circuit will be established which extends by Way of the test wiper 131, armature 116 and its resting contact, the interrupter contact of the rotary magnet 105, off normal springs 114, and the winding of the stepping relay 104 to By current flow over the above circuit the stepping relay 104 is again energized and again closes the circuit of the rotary magnet 105, which is therefore operated to advance the switch wipers into engagement with the next set of bank contacts. the stepping relay 104 is of course broken as before, and this relay therefore deenergizes again, "followed by the deenergization of the rotary magnet. This operation, in which the stepping relay and rotary magnet are energized alternately, will continue as long as the test wiper 131 engages busy or grounded test contacts. As soon as the wipbattery.

The circuit of ers arrive at the first idle trunk line, however, which we will assume to be the trunk line shown in the drawing and comprising conductors 120 and 122, the test wiper 131 will find no ground potential on the test which has been short cirpingrelay 104 toibattery. On account of the high resistance of said'relay 100, relay 104 is not operated. Relay 100, upon ener- 'gizing, connects the -groundedconductor 9 to the test Wiper 131 by means of its arma ture 116, thereby placing a ground potential upon the test contact 134 and its multiples in order to make the trunk line busy, and at the same time completing a circuit which extends by way of conductor 124, the winding of the switching relay 137, and the winding of the stepping magnet 138 of the line switch C to battery. The line switch C is a'rotary line or trunk selecting switch used in extending the trunk line to a first selector in the main exchange in the establishment of branch to main exchange connections, and the energization of the switching relay 137, which is operated only about half way due to the fact thatthe line relay of the line switch is not operated, serves to disconnect the branch trunk conductors 123 and 125 from their normal battery and grounded connections in the line switch. The switching relay 100 of the selector F also opens the vertical magnet circuit at its armature 117, the circuit being transferred to the release delaying relay 108, and at itsvarmatures 115 and 118 extends the incoming trunk conductors (S4 and 60 to the line wipers 130 and 132, it being noted that armatures 113 and 112 of relays 101 and 102, respectively, are in operated position.

'The calling main exchange subscriber has now established connection with the main to branch exchange trunk line comprising conductors 120 and 122, the connection having been established by means of the subscribers individual line switch, a first selector in the main exchange, the combination regular and toll transmission repeater E, and the special second selector F. Upon the-completion of the connection to the trunk lnie a circuit is completed for the double wound line relay 205 of the connector H which may be traced as follows: ground at G lower winding of relay 205, resting contact of armature 239 and the said armature, contact springs controlled by armature 251,

- conductor 154, normally closed contacts of keys K and K at the attendants cabinet, conductor 122, bank contact 135, wiper 132, Working confict of armature 113 and the said armature, working contact of armature 118 and the said armature, conductor 60, armature 43 and its working contact, upper right hand winding of the repeating coil R, resistance 77, armature 2 7 and its resting contact, lower winding of the electropolarized relay 15, resistance 78, lower winding of the repeating coil R, working contact of armature 46 and the said armature, conductor 64, armature 115 and its working contact, armature 112 and its working contact, wiper 130, bank contact 133, conductor 120, normally closed contacts of keys K and K conductor 163, normally closed contacts controlled by armature 247, armature 235 and its resting contact, andthe upper winding 205 in the connector H pulls up it closes a circuit forthe slow acting release relay 204 at its armature 234. Upon energizing, relay 204 connects ground G to conductor 164 at armature 231, thereby lighting the busy lamp at the attendants cabinet and also placing a ground potential upon the test contact 147 and its multiples in the banks of the automatic switches in the branch exchange which have access to the main exchange trunk lines. This renders the trunk line shown busy to these switches, and the lighting of the busy lamp of course indicates to the attendant operator that the trunk line is in use.

The apparatus is now in'readiness for the operation of the connector H in the branch exchange to complete the connection to the desired branch exchange line. When the calling subscriber operates his calling device in accordance with the next digit in the number a series of interruptions is produced in the circuit of the line relay 101 of the selector F as before, but now since the switching relay 100 has been operated the line relay causes no further operation of the selector switch but instead it interrupts the circuit of the line relay 205 of the connector at its armature 113. The line relay 101 therefore operates as a repeating relay and repeats the interruptions produced in its own circuit into the circuit of the line relay 205, which latter relay is accordingly deenergized a plurality of times and at each deenergization transmits an impulse of current to the vertical magnet 214 over the following circuit: ground at G, armature 234 and its resting contact, armature 232 and its working contact, armature 250 and its resting contact, ofl' normal springs 281 and 283, winding of the vertical magnet 214 and the winding of the slow acting relay 207 to battery. This is the circuit over which the first impulse is transmitted. At the first upward movement of the shaft the off normal springs are shifted and the circuit is completed by way of 01f normal springs 281 and 282, armature 242 and its Working contact (relay 207 being new in operated position), winding of the vertical magnet 214, and the winding of the slow acting relay 207 to battery. By the operation of the vertical magnet 214 the shaft of the connector H is raised step by step until wipers 273276,,inclusive, stand opposite the level of bank contacts in which is terminated the desired line. The slow act aeoasva 'tact of armature 240 and the said armature,

tenth level switching springs 289 and 290, and the upper winding of the ring out oli relay 210 to battery. Upon energizing, relay 210 establishes a locking circuit for itself. at its armature 255, and at its armatures 252 I .and 256 disconnects the ringing equipment ductor 164,

rotated the required and its own lower winding and closes the normally open contacts in the heavy talking conductors. Relay 210 also produces a number of other circuit changes, only one of which need be noticed now, which is the completion of a circuit for the slow acting relay 203 which extends as follows: grounded conarmature 254 of the relay 210 and its working contact, resting contact of armature 249 and the said armature, conduc-- tor 1.62, normally closed contacts of key K Fig.3, conductor 161, and the winding of the slow acting relay 203 to battery. Upon en ergizing, relay 203 produces changes which are of no effect just at present and which will be explained later on. When the transmission of impulsesto the vertical magnet ceases the slow acting series relay 207 falls back and at its armature 242 transfers the operating circuit to the rotary maginet 215.

' Thecalling subscriber may now operate his calling device in accordance with the final :digit in the desired number, thereby producing another series of impulses in. the

circuit of the line relay 101 of the selector 4, which are repeated as before into the circuit of the line relay 205 of theconnector H. The line relay 205 is accordingly again deenergized a plurality of times and transmits impulses to the rotary magnet 215 over the following path: ground at G, armature 2534 and its resting contact, armature 232 and its working contact, armature 250 and its resting contact. oft normal springs 281 and 262. armature 242 and its resting contact, resting contact of armature 259 and the said armature. winding of the slow acting relay 212, resting contact of armature 271 and the said armature, and the winding of the rotary magnet 215 to battery. By the operation of the rotary magnet in response to the transmission of impulses over the above circuit the connector wipers 273275, inclusive, are amount and are finally brought to rest in engagement with the particular set of bank contacts in which is terminated the line of substation 1, these bank contacts being the ones indicated in the drawing by the reference characters 277280, inclusive. The relay 212 is energized in seagainst the possibility of operated while the test wiper 274 is passing various circuit he may wait on the line,

its armature 263' relay 212 connects the test wiper 274 to the test relay 211, and at its armature 265 closes a shunt around the backcontact of armature 259 in order to guard the test relay being over busy test contacts.

Whenthe' test wiper 274 comes to rest in engagement with test contact 27 8, ifthe called line is busy the test wiper will find a ground potential upon the said test contact and the test relay 211 will be energized. The rotary movement having stopped, the slow acting series relay 212 is now deen ergized and a locking circuit is established for the test relay 211 which extends ,from

the grounded test contact 278 by way of test wiper 274, armature 258 and its working contact, normally closed contact springs controlled by armature 263 of relay 212, armature 269' and its resting contact, and the winding of the test-relay 211 to battery. In energized position relay 211 opens the rotary magnet circuit at its armature 259, opens the circuit of the switching relay 213 at its armature 260, and .at its armature 262 connects a lead from the busy signalling machine Q to the lower heavy line conductor. As a result of the latter'operation. a'busy signal is transmitted in the well known manner to the calling subscriber in the main exchange, who is thus advised that the desired line is engaged and is for the time being inaccessible. It may. be mentioned that the tone from the busy signalling machine passes back overthe lower heavy talking conductor to the repeating coil R T at the repeater E, where it passes through the right hand windings of the repeating coil and returns by way of the upper heavy talking conductor, the condenser 292 -at the connector H, working contact of armature 257 and the said armature, and the windings of relays 209 and 213 in parallel to battery. The return through the condenser 292 is in parallel with the branch which extends through the upper winding of the line relay 205 and is provided. in order to increase the loudness of the busy signal.

The calling subscriber'may now hang up his receiver, intending to release the switches and wait for the called line to become idle before he calls it again; or, if he so desires, the operation of the connector H in connecting through and completing the connection being the same in "either case. We will assume therefore that the calling subscriber does not hang up" but waits until the busy condition is terminated. When the called line becomes disengaged, ground is removed from thetest contact 27 8 and the test relay 211 will be deenergized.

.rotary magnet circuit at its As a result a circuit is completed for the switching relay 213 which extends as follows grounded conductor 164, resting con tact of armature 260 and the said armature, lower winding of relay 213, resting contact of armature 263 and the said armature, test wiper 274, test contact 278, conductor 304, winding of the switching relay 301, and the winding of the stepping magnet 302 of the line switch C to battery. Relays 213 and 301 are energized in series by the closure of the above circuit and the latter relay operates its armature sufficiently to disconnect the line conductors extending to substation A from their normal battery and ground connections in the line switch. Owing to the fact that the line relay of the said line switch is not energized, relay 301 is not operated oompletelyand the lines are not connected through to the'line switch wipers. At connector H, when the switching relay 213 pulls up, it establishes a locking cir cuit for itself at its armature 268, opens the armature 271, grounds the test wiper 274 at its armature 270, and at its armatures 266 and 272 closes the heavy talking conductors through to the line wipers 273 and 276.

When the switching relay 213 locked itself at its armature 268 it also completed a circuit for relay 209 which is energized in parallel with the upper winding of the said relay 213. Relay 209 opens the operating circuit at its armature 250, prepares a circuit for relay 206 at its armature 248, prepares a circuit for relay 200 at its. armature 299, and at its armature 249 breaks the circuit of the slow acting relay 203. The breaking of the latter circuit is of course followed by the deenergization of relay 203 but the explanation of the results produced by the falling back of this relay will be deferred for a moment in order to finish with the operations of relay 209. In addition to the circuit changes already mentioned this relay 209 reverses the. heavy incoming line con uctors 163 and 154 by means of its armatures 247 and 251. In order to make this a little more clear it may be explained that the line conductor 163, which before the operation of relay 209 extended through to the upper line wiper 273, is connected by way of the windingof low resistance series vrelay 202 and armature 251, and its working contact to the lower line wiper 276; while the lower line conductor 154, which before relay209 is operated extends to the lower line wiper 276, is transferred by way armature 247-and its working contact to the upper line wiper 273. When the line explained, as regards'their connection to the line wipers, they are. also reversed as regardsyth'e'ir connection to the upper and lower windings of the line relay 205, and it follows that the direction of current flow in these conductors will be reversed. Consequently, the direction of current flow in the lower winding of the electropolarized relay 15, at repeater E, which relay is included in the line relay circuit, will be reverse-d also; and now, since the two windings of the said electropolarized relay assist each other, the relay will be operated. When the current flow in the trunk is reversed relay 15 first operates its armature 26, thereby short circuiting the high resistance 74, and the relay then pulls clear up by the complete cnergization of its upper winding. At its armature 27, relay 14 breaks the circuit through its own lower winding and at the working contact at this armature connects the upper trunk conductor by way of the battery feed relay 16 to battery. At the same time, at its armature 28, the lower line conductor is connected to ground. It should be observed that since the lines have been reversed at the connector H, relay 16 and the upper winding of the line relay 205 are both connected to the same side of the trunk and relay 16 accordingly is not energized at this time.

The operations at the repeater have not been completed, but further explanation thereof will be deferred while certain other operations which take place at the-connector H are explained. It was said before that when the relay 209 pulled up it broke the circuit of the slow acting relay 203. Upon deenergizing, relay 203 completes a circuit for the slow acting relay 206 as follows: grounded conductor 164, armature 229 and its resting contact, armature 248 and its working contact, and'the winding'of relay 206 to battery. Upon energizing, relay 206 establishes a locking circuit for itself. at its armature 236, prepares a circuit for relay 208 at its armature 237, and at its armatures 235.and 239 disconnects the line relay 205. This latter operation leaves a clear talking circuit through the connector with no bridges across the line whatever. When the line relay 205 deenergizes, the slow acting release relay 204 would de ergize also and bring about the release of the connector were 1t not for special provisions which are introduced to prevent it. When the relay 206 pulls up, at the same time that the line relay is disconnected, relay 200 is connected to the ower line conductor as follows: conductor 154, working contact of armature 299 and the said armature, armature 238 and its working contact, resting contact of armature 224 and the said armature, upper and lower windings of relay 200 in series, and the resistance 294 to ground. Conductor 154 is the line conductor which at the repeater E is connected with the batter feed relay 16, or with battery by way of resistance '80 if the ringing operation is taking place, and

the closure of the contact at armature 222" a holding circuit is completed for the slowacting release relay 204 which is thus maintained energized to prevent the release of the connection. The resistance of the circuit through relay 200 and the high resistance 294 is of course so great that the bat-' tery feed relay 16-at the repeater E operated.

. Returning now to the repeater E, the exis not planation of the operations thereat which result from the energization-of the electropolarized relay 15 when the trunk conductors are reversed at the connector will be proceeded with. l/Vhen relay 15 pulls up it breaks the circuit of relays 20 and '21 at its armature 25 and both of these relays deenergize. Relay 21 falls back first, and at its armature 44 completes a circuit for the relay 22 as follows: grounded conductor 9, armature 25 and its working contact, armature .44 and its resting contact, and the winding of relay 22 to battery. Upon energizing, relay 22 looks itself at its armature 47 and at its other armatures prepares a numberot circuits which remain open at other relay contacts for the time being.

When relay 21 deenergizes it also breaks the line conductors at its armatures 43 and 46 and at the resting contacts of these ar-.

- matures closes the ringing circuit. Although the upper line conductor 60 is disconnected from the battery feed relay 16 by this operation, relay 200 at the connector H does not deenergize, its circuit being closed by way of resistance at armature 43. By the operation of the automat c ringing equipment shown immediately below the repeater E, Fig. 1, ringing current from the generator Gen is intermittently projected out over the called line to ring the bell at substation A. The ringing circuit is substantially the same as the ringing circuits in common use and may be traced without difliculty from the generator by way of the upper winding of the ring cut off relay 21, conductor 64, conductor 120, conductor 163, and line conductor 305 (the lines having been reversed in the connector H) to substation A, where the circuit continues through the bridged ringer at the-substation and returns by way of conductor 303, conductor 154, conductor 122.

conductor 60, and through the resistance 80 tery to the ungrounded pole of the exchange battery It 1s noted that the ringing circuit includes relay 202 at the connector H, butthis relay 1s of relatively low resistance and moreover is shunted'by a non-inductive resist- 7 ance; accordingly, it does not respond to the ringing current. Attention is also called to the fact that there is a low capacity condenser bridged around the open contact in the lower line conductor at armature 46. 75 This permits suiticient ringing current to leak back in the scriber to give direction of the calling sublnm the usual rlnging current induction, so called, which indicates place. so

that the ringing operation is taking When the subscriber at substation A removes his receiver from the hook to answer the call the ring out off peater E is operated in the usual an known manner and mature 45 establishes relay 21 at the red well upon attracting its ara locking circuit for itself; Relay 21 also breaks the ringing circut at the back contacts of its armatures 43 and 46, and at the working contacts of these same armatures closes the heavy talking condu'ctors. pleted, the transmitter at substation The connectionhaving been com- A is supplied with talking current through the right hand windings of the repeating coil R, thetwo resistances]? and 78, and the windof the battery feed relay 16. The batfeed relay 16 is therefore energ zed and at its armature 29 closes a circuit for the reversmg relay 18 winch, upon energizing, reverses the conductors 70 and 71 as regards their connection with. outgoing trunk conductors 62 and 63 and also therefore asregards their connection with the windings of the double wound line relay 101 in the selector F the lowerwinding of this relay, ho being short circuited by the ground c wever, onnection at armature 32 of relay 17. This operation reverses the direction of current flow in the calling line and is the usual provis on adopted for the purpose of operating a or coin collect device.

meter Or in case the calling party is some operator, other than a toll operator, who is required to use the regular exchange trunk ng system for calling, the reversal of the current operator supervision.

nection trouble operators do not usually have will give the calling It is noted in this conthat the information operators and access to the toll service trunking system but are required to use the regular local or subscribers trunking system; and also of the operators-at private bran changes. 3--

this s of course true ch ex- 'At 'the connector-H, when the called subscriber answers his telephone. the relay'202, which is in series with one side of the line,

is energized and closes a circuit for relay 201. Upon energizing-relay 201 closes a circuit for the slow at its armature 225, and at its arm'atu acting release relay 204' disconnects relay 200 from the line.

This clears the talking circuit by removing the high resistance connection to ground through relay 200 which was used until now in order to prevent the release of the connection. Relay 201 also closes a circuit for relay 208 at its armature 226 and this relay, upon energizing, establishes a locking circuit for itself at its armature 246. In addition, relay 208 prepares a circuit for the supervisory lamp at the attendants cabinet by means of its armature 243.

\ established The complete connection has now been and the calling and called subscribers can converse as desired. The trans mitter at the called station is supplied With talking battery through the winding of battery feed relay 16 at repeater E, as stated, while the transmitter at the calling substation is of course supplied with talking battery through the upper winding of the line relay 101 in the selector F. The circuit arrangements provide for hook supervision by the called subscriber, not only at the attendants cabinet in the private branch exchange, but also at an operators position in the main exchange, provided the calling party is an operator. The latter supervision is of course controlled by the battery feed relay 16 at the repeater which controls the reversing relay 18. The supervisory lamp at the attendants cabinet is controlled by the relay 202 at the connector. If the called subscriber should hang up his receiver relay 202 will fall back whereupon relay 201 will deenergize and now, since relay 208 is in operated position, a circuit for the supervisory lamp will be completed as followsf ground at G, armature 230 and its resting contact, armature 223 and its resting contact, armature 243 and its working contact, conductor 160. and the supervisory lamp at the attendant operators position to battery. It is noted that whenever relay 201 is deenergized relay 200 is again connected from the lower side of the line to ground in order to hold up release relay 204 and prevent the release of the connector. If the calling subscriber should replace his receiver the connection is released by the deenergization of the line relay 101 at the selector F. The release of the connector H under these circumstances will no doubt be readily understood, and at any rate, it need not be explained in detail now because the release of this switch will be explained fully later on; it is noted, however, that when armature 113 of the line relay 101 is retracted it breaks the lower line conductor extending to the connector and causes relays 200 and 204 to fall back, the latter relay then closing the circuit of the release magnet 216. The release circuit at the selector F, however, is somewhat different from the usual release circuit and may be explained now to good advantage. When the line relay 101 falls back it closes a circuit for the slow acting relay 106, which, upon energizing, grounds the release trunk conductor 9 and also opens release magnet 108. It the slow acting release an instant later, ground is not removed from conductor 9 and the release magnet CllClllil is not closed. Relay 102, however, opens the circuit of the slow acting relay 106 and when this relay deenergizes ground is removed from conductor 9 and the release magnet circuit is closed. Relay 106 therefore operates to delay the release of the selector F and the switches in the main exchange. This delaying operation is of no particular consequence in connection with the circuits herein illustrated but is necessary under certain conditions and with certain types of equipment in order to insure that the connector switch at the branch exchange be restored to normal po sition before the switching relay of the line switch associated with the trunk line at the main exchange is permitted to deenergize. It is noted that as long as conductor 9 is grounded and the selector F is held in operated position the switching relay 137 f the line switch C will be maintained energized.

the circuit of the follows that when relay 102 falls back Trans caved connection.

As is explained in the preceding paragraph, if the calling subscriber hangs up his receiver the connection will be released; but it will be convenient, in order to proceed with the explanation, to assume that the calling subscriber desires to obtain connection with some other line in the branch exchange, in' Which case he will not hang up his receiver. It happens quite frequently, as is well understood, that the particular person wanted at a private branch exchange telephone may be temporarily absent in some other department. or it may be found after the called subscriber has answered that the matters under consideration can best be dealt with by some other person. In either case it is desirable to have the attendant at the branch exchange transfer the connection and thus relieve the calling subscriber of the trouble involved in disconnecting and calling the entire number over again. In such case the party first called will flash the op erator by working his receiver hook in the well known manner. This operation causes the relay 202 at the connector to deenergize intermittently and interrupt the circuit ofv relay 201. Each time the latter relay falls back it closes a circuit for the supervisory lamp at the attendant operators position over a path previously traced. It should be remembered that Whenever relay 201 deenergizes it also connects relay 200 to one side of the line and this relay of course alkey.

known manner. "round G from the conductor 164 and as a ways closes the contact at its armature 222 in order to maintain the release relay 204 energized.

When the attendant operator sees the supervisory lamp flashing she will answer by throwing her key K to listening position. This bridges the operators head set across the heavy talking conductors of the trunk and" the operator is able to converse with either or both of the subscribers and find out what is wanted. Assuming now that the calling subscriber desires to have the call transferred to some other station in the branch exchange, as soon as this information is imparted to the operator the called party at substation A will replace his receiver. Relays 202 and 201 now fall back. and since the key K at the operators position is in listening position, the latter relay connects the lower winding of relay 200' in bridge of'the line over the following path: from the lower trunk conductor 154 by way of armature 238 and its working contact, resting contact of armature 224 and the said armature, lower winding of relay 200, conductor 156, and contacts of key K to the upper trunk conductor 163. This relay is connected across the line in order to maintain the same closed should the operator afterwards restore her key, as will appear hereinafter. Relay 200 is energized by current from the battery feed relay at the repeater E and is completely operated, closing a locking circuit for itself at its armature 220 which is independent of the contacts at the At its armature 221 relay 200 also con nects ground to conductor 160 and thereby lights the supervisory lamp at the operators position.

Having ascertained the number that the' calling party desires to be transferred to,

the attendant operator will throw her key K to the. call in position. By the opera t-ion of the key the heavy talking conductors of the trunk extending through the operators position are broken, resistance 170 is connected in bridge of the section of the trunk which extends in' the direction of the calling subscriber, and the operators head set including the calling device S is connected in bridge of the section extending to the connector H. When the trunk line is opened the section extending toward the connector is of course cleared from all battery connections and relay 200 is deenergized, followed by the deenergization of the slow acting release relay 204. The deenergization of the latter, relay closes the circuit of the release magnet'216 and the connector H is restored to normal in the usual and'well Relay 204 also disconnects i' esult all the relays i the connector which were locked up to thi conductor are deenergized. This includes relays 206, 208, 209,

210 and 213. When the slow acting relay 206 falls back the line relay 205 is again connected in bridge of the trunk conductors 163 and 154, and since the operators set bridged across the trunk at the attendants cabinet, the line relay is energized. The

slow acting release relay 204 then pulls up also, again grounds conductor 164, and prepares the connector for the vertical operation thereof. ,In addition to relays 205 and 204, relay 203 is also energized at this time, its circuit being closed over conductor 161 at the key K The operator may now operate her calling device in accordance with the digits in the local number of the desired line. When the dial is operated in accordance with the first digit in the number the circuit of the line relay 205 is interrupted a plurality of times and this relay transmits a series of impulses to the vertical magnet 214 over circuits previously traced. By the operation of the vertical magnet the wipers 273-276, inclusive, are raised step by step and are brought to rest opposite the desired level of bank contacts. The slow acting relay 207 is energized in series with the vertical magnet as before explained and with the same results, except that in the present case, since relay 203 is in operated position, relay 207 does not close the circuit of the ring out off relay 210 and *this latter relay remains deenergized. When the operator calls the next and final digit in the number the line relay 205 sends a series of impulses to the rotary magnet 215.

which operates to rotate the wipers 273-276, inclusive, into engagement with the particular set of bank contacts in which the desired line is terminated. During the rotary movement of the switch the slow acting relay 212 is of course energized in series with the rotary magnet and connects the test wiper 274 with the test relay 211 in order that when the called line is finally found it may be tested in the manner already explained. This operation having been gone over already, it will be assumed that the called line is found to be idle, in which case, when the slow acting relay 212 deenergizes, the switching relay 213 will pull up in series with the switching relay of the line switch which is associated with the connected called line.

These operations have all been described and may be passed over without further consideration. It should be recalled, however, that when the switching relay 213 energizes it establishes a locking circuit for itself at its armature 268, thereby also closing a circuit through the reversing relay 2 S). Upon energizing, relay 209 does not'open the circuit of relay 203 as before, because conductor 161 is now grounded at key K. In the present case, then, relay 209 simply reverses the trunk conductors 163 and 154 at the connector. By this operation relay 202 15 inlit] in Fig. 1.

cluded in the circuit of the line relay 205 and is energized, thereby closing the circuit of relay 201 which energizes also.

The call has now been extended to a second line in the private branch exchange and since the ring cut oil relay 210 has been left deenergized, ringing current will be projected over the called line from the connector switch. In this connection it may be stated that conductor 295 is a lead coming from a signalling machine similar to the one shown Having completed her work in setting up the connection, the attendant operator may now either wait on the line to make sure that the right party is obtained, or she may restore her key at once and leave the calling subscriber to control the connection. lVe will suppose first that she waits on the line until the called party answers. When the receiver is removed from the hook at the called station the ring out off relay 210 is operated, establishes a locking circuit for itself at its armature 255, opens the ringing circuit at the back contacts of its armatures 252 and 256, and at the working con tacts of these armatures completes the talking circuit. Relay 206 has not yet pulled up and the trunk conductors are open at the operators position, and it follows therefore that the. transn'litter at the called station will be supplied with talking battery through the windings of the line relay 205 whichis still in bridge of the line at the connector. The operator will now talk with the called party and if everything is O. K. she will restore the key K to normal. This operation removes all bridges at her position and connects the line through as it was originally. In addition, the restoration of key K breaks the circuit of relay 203 which upon deenergizing closes the circuit of the slow acting relay 206. Upon energizing, relay206 disconnects the line relay 205 from the line and the called station is supplied with talking battery from the repeater E. Relay 202 holds up in series with the line circuit and relay 201 is therefore held energized also to maintain the release relay 204 energized in order to prevent the release of the connector. The circuit conditions are now the same as in the case where the calling subscriber established the connection himself, in the first place.

In order to explain the operations fully it will now be assumed that after the operator has extended the connection to the second called line she restores her key K at once, without waiting for the called party to answer. On restoring the key.'the lines are cut through and relay 203 is decnergized as explained. When relay 203 falls back it closes the circuit of relay 206 which energizes and cuts otl the line relay 205. At the same time. relay 206 connects relay 200 to the lower line conductor by means of its armature 238, and relay 200 is energized by battery from the repeater E. As before explained, this relay operates only enough to close the contact at its armature 222 in order to hold up the slow acting release relay 204.. It will be noticed that when a call is transterred the ringing current is necessarily applied to the second called line from the conneetor H, rather than from the repeater E, as is the case when the connection is established by the main exchange subscriber himself. Since the attendant operator is involved in the establishment of the transferred connection, it is desirable that she be given supervision, and it will be observed now that since the ring cut off relay 210 is deenergized, the ringing operation being now going on, the supervisory lamp is lighted over the following ciriuit: grounded conductor 164, working contact of armature 268 and the said armature, armature 257 and its resting contact, armature 253 and its resting contact, resting contact of armature and the said armature, conductor 160,

l and the supervisory lamp. to battery. While the ringing operation is taking place the calling subscriber (or the attendant, it' she is on the line) is given the usual ringing current induction by means of the path which extends from the line wiper 273 by way of the condensers 293 and 292 to the upper line conductor just back of the open contacts at the ring cut oil relay 210. \Vhen the called partyanswers, the ring cut of? relay 210 pulls up, locks itself as before, discon nects the ringing equipment, and closes the talking circuit. Relay 210 also opens the circuit of the supervisory lamp at its armature 254, and the lamp is extinguished to notify the attendant operator that the called party has answered.

The release of the connection is under the control of the calling subscriber and when he replaces his receiver all the automatic switches will be restored to normal as previously explained. It is understood, of course. that in case the called party does not an swer, as indicated by the continuation of the lighted condition of the supervisory lamp, the operator may come in on the line again, and if necessary, can release the connector as before by throwing her call in key. The connector can then be reopcrated to estab lish connection with some other line.

The foregoing describes the operations which take place in transferring a call to another local line, it being assumed that the second called line is idle. As stated heretofore, if the line to which the call is transferred is busy the operations incident to this condition of the called line are the same, so far as the operation of the test relay and the transmissionof the busy signal to the calling party is concerned, as in the case previously described where the calling subscriber established the connection himself. There are, however, certain operations having to do with the release of the connector H by the attendant operator when a transfer has been attempted and the line found busy, which have not yet been touched upon and which will now be explained. It will be assumed that a call has been completed to a line in 213. are at normal.

V the batteryv feed relay 16 at Having received the busy signal, the operator maynow restore her key K to normal. This disconnects the operators head set and calling device and connects the trunk line through as it was originally. Relay 203 is also deenergized by the restoration of the key, but relay 206 does not pull up at this time, because its circuit is opened at armature 248 of relay 209. For the same reason, that is, because relay 209 is in normal position, it will be clear that the incoming line conductors have not yet been reversed at the ,connector and it follows that the main and branch exchange batteries will be connected in series over the trunk line. To make this a little more clear it may be explained that the repeater E and the lower winding of the line relay 205 at the connector are now connected to the same side of the line, which of course is also true as regards the grounded resistance 7 8 at the repeater E an the upper winding of the line relay 205. It follows that relays 16 and 205 are energized in series, the energization of the latter relay being of course effective to maintain the connector H" in operated position. The calling subscriber can now hear the busy signal which notifies him that the line to which it has been attempted to transfer his call is busy. The operator can leave the circuits in this condition if she so desires, and if the called line becomes idle the connector will cut through and the connection will be completed as in ordinary cases. Or if the calling subscriber hangs up his receiver, the entireconnection will be released. Both these situations have been gone over before. vOn the other hand, if the operator considers it necessary or desirable to assist the calling subscriber further she may come in on the line and talk to him by throwing the key K to call out position. This operation opens the trunk line at the attendants position and thus cuts off the by way of resistance the connector are now in normal position, it

busy signal coming from the connector H so that the parties can talk together without interference. It should be mentioned also, that the opening of the linebyfthe call out key does not cause the release of the connector H due to the fact that a circuit is completed for the lower winding ofthe relay 205 149, which is connected to the lower trunk line conductor at the lower contacts of the key. Suppose now that the attendant desires to release the connector from the busy line and try some other number. It will be plain that she cannot do this by merely throwing the ke K to call in position as this would simp y bridge her head set and calling device across the trunk line and the line relay 205 would stay energized. Special means is therefore necessary to accomplish the release under the conditions now existing, and to meet the requirements the release key is provided. \Vhen the key K is thrown to the release position the two conductors of the trunk line are opened and as a result the line relay 205' and the slow acting release relay 204 are deenergized and the connector is released. At the same time a circuit is completed by way of conductor 159 and the tenth level switching springs 289 and 29.0 for the rin cut-off re lay 210 which upon energizing closes the circuit of relay 203 over conductors 162 and 161. Upon energizing, relay 203 extends conductor 157 which is now grounded at the release key, to relays 209 and 213 which are accordingly energized also., Relay 209 performs its usual function of reversing the line and also breaks the circuit of relay 203, which falls back an instant later and closes the circuit of relay 206. 'Upon energizing, the latter relay disconnects the line relay 205 and connects relay 200 to the lower side of the line. The release key may now be restored to normal, in fact, it need only -be operated momentarily, and the trunk line conductors are again connected through, ground being disconnected from conductors 159 and 157 at the same time. Relay 200 now pulls-- up from battery at the repeater and closes a 1 circuit for the slow acting release relay 204 I which accordingly energizes and connects groundto conductor 164. As a result of the latter operation relays 206, 209, 210 and 213, all'of which it will be noticed are slow acting, are locked up and remain in energized position. Although the shaft and wipers of will be observed that the circuits of the connector so far as the relays are concerned are in the condition of having completed a connection with a called line which has not, answered. In short, the connector is in the ordinary ringing position and if the attendant should not come back on the line no particular harm is done because the circuits are in condition to maintain disconnect supervision at any operators cord circuit who may be calling and the connection can not become tied up. This condition will be considered more fully later on.

According to the previous assumption, however, the call is to be retransferred and the attendant operator may now proceed to call another number in the branch exchange by throwing the key K to the call in position. By this operation the trunk line conductors are opened and her head set and calling device are bridged across the conductors extending toward connector H. The opening of the trunk line causes relay 200 to deenergize, and the release relay 204 is therefore deenergized also to remove ground from conductor 164. All the various relays in the connector which have been locked up are now deenergized also, and relay 206 again connects the line relay 205 .acrossthe conductors of the trunk line. The operators head set and calling device being in bridge of the trunk line the line and release relays 205 and 204 are now energized again .and the connector is all ready to be reoperated. The operations which take place when the attendant operator sets up a local connection by use of her call in key have already been explained in detail.

Rotary operation of connector.

In the foregoing pages I have explained howa connection is extended from a line in the main exchange to the line of substation A in the branch exchange, the latter being a private or individual line. The connector H, however, is what is known as a rotary connector, and may have access to-a num ber of groups of lines or trunk lines as well as to individual lines like the one shown in the drawing. For example, if the private branch exchange is located in a manufacturing establishment a certain-department may have a plurality of lines extending thereto, all of which are reached by calling the same telephone number, the number called being the number of the first line in the group. An arrangement of this kind is common and well known in the art. In order to take care of the rotary feature the connector H is provided with an additional test wiper which is the wiper 275, and also with an additional bank of test contacts which are associated with the said test wiper. In Fig. 5, I have shown all the test contacts in a certain level, and the way in which they may be connected in order to take care of the grouping of lines. The upper row of contacts are the regular test contacts which are engaged by the test wiper 274, while the lower row of contacts are the extra test contacts which are engaged by the special test wiper 275. If it is desired to combine certain lines into a group, the two test contacts associated with each of the lines except the last are connected together. The test contacts associated with'the last line of each group are left disconnected, as are also the test contacts which are associated with the individual lines, Thus, in Fig. 5, with the test contacts connected as shown, the first four lines in the level constitute a group; the next three lines are individual lines; and the last three lines constitute a second group.

The operation of the connector H as a rotary connector will now be briefly explained. It will be .assumed that a call is initiated by the subscriber at the main exchange, and that the connector H at the branch is used to complete the connection, all as previously explained, except that in the resent ease the called number is the number assigned to a group of lines rather than to an individual line at the branch exchange. VVhen the connection is completed to the first line of the group, if the line is busy there will be a ground potential upon the test contact with which the test wiper 274i is in engagement, and the test relay 211 will beenergized. Relay 2111, upon energizing, establishes a locking circuit for itself and performs other circuit changes which have already been explained. Since the regular test contact and the special test contact which are associated with each line in the group except the last are tied together, the test contact which is engaged by the special test wiper 275 will also have a ground po tential upon it, and a circuit is therefore established for relays 208 and 207 as follows: from the grounded test contact, by way of test wiper 275, restingv contact of armature 264i, interrupter contact of the rotary magnet 215, armature 261 and its working contact, lower winding of relay 208 and the-winding of the slow acting re lay 207 to battery. Relays 207 and 208 are energized by current flow in the above circuit and the latter relay, upon energizing, establishes a locking circuit for itself and relay 207 at its armature 244 in an obvious manner, and at its armature 245 closes a circuit for the rotary magnet 215 as follows: grounded conductor 1G4, armature 236 and its resting contact, armature 24:5 and its working contact, resting contact of armature 271 and the said armature, and the winding of the rotary magnet 215 to battery. The rotary magnet is accordingly energized and operates to rotate the wipers of the connector into engagement with the next set of contacts in the group. Near the end of its stroke the rotary magnet breaks the locking circuit of relay 208 at its interrupter contact. Relay 208 at once deenergizes and breaks the circuit of the rotary magnet which then deenergizes also. The operation now depends upon whether the line associated with the second set of contacts in the group is reente /a 1B busy or not. If the line is busy there will ator to know whether the party called for is be a ground potential upon both contacts as located in the main exchange or in a branch before, and relay 208 wil again be energized, exchange. To complete the required conwith the result that the rotary magnet is nectiou, then, the operator will simply take again operated to advance the wipers into an idle one of her cord circuits and will plug engagement with the next set of test coninto the jack of an idle outgoing toll service tacts. As soon as an idle line is reached trunk. The circuits of the toll'service trunkneither test wiper will find a ground potening system are preferably similar to those tial, the rotation of the switch will stop, shown in my copending application prethe test relay 211 will deenergize and the viously referred to, and it may be stated at -7 switching relay 213 will be energized as this point that the toll first selectors are subpreviously explained to complete the connecstantially the same as the first selectors tion. It all the lines in the group are busy which are used in the local trunking system; the rotation of the switch will continue until in particular, it may be mentioned that the the last line of the group is reached, wheretoll selectors are of the type which are .conupon, since the two test contacts associated trolled over the two sides of the line in series with the last line are not connected together, rather than over a separate conductor. Asthe special test wiper 275 will find no ground suming then that the toll service trunk which potential and the rotation will stop. Test terminates in the jack J, 6, is the trunk wiper 274, however, is still resting on a to be used,- when the operator plugs into the grounded test contact, for the last line in jack the line relay of the toll first selector the group is busy, and the test relay 211 will will pull up over the two sides of the trunk remain energized. The circuit through reline in series and the slow acting release relays 208 and 207 being now permanently lay of the selector will be energized in the broken, the slow acting relay 207, which usual manner to prepare the switch for opermaintains its armatures in operated position ation. The operator will now throw her during the rotation of the switch, now decalling device key whereby her head set and energizes and at its armature 241 closes the calling device is bridged across the two lead to the busy signalling machine. It w ll strands of the cord circuit in use. The cirbe understood that relay .207 is included 1n cuits are now in readiness for the calling of the circuit of relay 208 for the sole purpose the required number. When the calling deof maintaining this busy signalling circuit vice is operated in accordance with the first open while the switch is rotating, it being digit a series of interruptions is produced in necessary to do this because the test relay 211 the circuit of the line relay of the selector is energized before the rotation starts and D and the said selector is accordingly operit is not desired to "give the calling party a ated in the usual manner to raise its shaft busy signal unless all the lines in the group step by step until the wipers stand opposite are busy. the level which is assigned to the bI'EglClfl clif- Q ciange trun in" s stem. At t e en 0 t e to b'mnch exchange comwotum' vertical movem e nt of the selector the 'usual Having described the operations involved trunk selecting movement is initiated and in establishing a connection from a local subthe wipers ofthe selector are rotated autoscriber in the main exchange to a subscriber matically until they arrive at the contact in the branch exchange, it will be convenient set associated with an idle trunk line. Asnow to explain what takes place when a toll suming that the trunk line comprising conoperator calls a subscriber in the branch e'xductors 11, 12, and 13, which extends to the change, with a view to pointing out wherein combination regular and toll transmission the operations differ from the operations repeater E, Fig. 1, is the first idle trunk already described. We may assume that theline, the wipers of the toll selector will be toll operator in front of whom the jack J, brought to rest in engagement with bank Fig. 6 appears has received a long distance contacts 5, 6, and 7 and it follows that when call from some distant point which is dithe switching relay of the toll selector operrected to the subscriber at substation A in ates the line conductors of the toll service the branch exchange. As previously extrunk will be extended by way .of the line plained, the present system provides for uniwipers of the toll selector, bank contacts 5 form routine operations on the part of the and 7, and conductors 11 and 13 to the left toll operator regardless of whether she is hand windings of the repeating coil R, calling main exchange or branch exchange whence they may be traced in the manner subscribers, and itwill be understood therepreviously explained through the repeater fore that the toll operator is not required to E tothe line relay 101 of the selector F. perform any unusual acts when calling a- "When the trunk is extended into connecbranch exchange subscriber or to discri'mtion with the repeater E as just explained, inate in any way between subscribers in the the line relay 101 of the selector F is enermain and branch exchanges. As a matter gized over the two sides of the trunk line in of fact, it is not necessary for the toll operseries and closes a circuit for the slow aeting release relay 102. Upon energizing, relay 102 prepares the selector for operation in its vertical movement, and also places a ground upon the release trunk conductor 9. By the latter operation a ground potential is placed upon test contact 3 and its multiples in the banks of the local first selectors having access to the repeater E, whereby the said repeater is made busy. At the same time, a ground potential is placed on test contact 6 and its multiples in the banks of the toll first selectors which have accessto the repeater. This renders the repeater E busy to all toll selectors except the selector in use; and as to the operated selector, the test. wiper of such selector is now in engagement with the test contact 6 and a holding circuit is completed in the usual manner for maintaining the switch in operated position.

The foregoing operations are substantially the same as the ones described in the case where the call was extended by the local subscriber in the main exchange, except that now the repeater E has been seized by a toll selector having access to the trunk line comprising conductors 11, 12 and 13, whereas in the former case the repeater was seized by a local first selector having access to the trunk line comprising conductors 8, 9, and 10. It will be observed now, that the holding circuit for the toll first selector includes the relay 19 at the repeater, and this relay accordingly energizes in series with the switching relay of the toll first selector. At its armature 39 relay 19 prepares a circuit for relay 22, and at its armature 4.0 closes a circuit for relay 17. Upon energizing,.relay 17 breaks the short circuiting connections normally existing around the resistances 81 and 82 by means of its armatures 31 and 35, respectively, and at its armature 32 ground connection which is provided for short circuiting the lower winding of the line relay 101 when the reversing relay 18 is operated on local connections. Relay 17 also prepares a circuit for the ring down alternating current relay 23 at its armature 30 and prepares other circuits at its armatures 33 and 34 which will be mentioned hereinafter. Relays 19 and 17 are relays which operate only on toll connections and it will be understood that these relays are provided in order to suitably alter the circuits of the repeater to enable it to perform the functions of a toll transmission repeater when handling this class of connections. In addition to the foregoing operations a flow of current is established in the polarizing winding of the electropolarized relay 15, and at the same time relays 20 and 21 are energized with the usual results.

The toll operator may now operate her calling device in accordance with the remaining digits in the number, whereupon the selector F and the connecto H are opbreaks the erated precisely as in the case previously explained to complete the connection to the line of substation A. In order to fully explain the operations it will be assumed now that the line of substation A is busy when called. Under these circumstances the busy test relay 211 at the connector H will he energized and locked up by Way of the test wiper ofthe connector, and a busy signal will be transmitted in the usual manner back to the calling toll operator. \Vhen the operator hears the busy signal she may of course withdraw the plug and release the connection, but ordinarily she will find it more convenient to simply restore her calling device key and wait until the called line becomes idle. tVhen the key is restored the supervisory relay at the operators cord circuit is bridged across the two strands of the cord in place of the operators head set and calling device and thus maintains the circuit of the line relay 101 closed and prevents the release of the connection. It should be stated at this time that the supervisory relay is preferably a polarized connected that it is not operated at this time. It follows that the supervisory lamp at the operators cord circuit will not be lighted.

When the called line becomes idle the test relay 211 is deenergized and the switching relay 213 is energized to complete the connection at the connector, all as previously explained. When the switching relay 213 is energized it establishes a locking circuit for itself and at the same time closes a circuit for the reversing relay 209. Upon energizing, relay 209 reverses the trunk conductors 163 and 154, incoming to the connector H, and thereby reverses the direction of current flow in the lower winding of the electropolarized relay 15 at the repeater E. The latter relay is accordingly operated, locks itself to the grounded conductor 9 at its armature 26, cuts out its own lower winding at the back contact of its armature 27. and at the working contacts of armatures 27 and 28 connects the inner terminals of the right hand repeating coil windings by way of resistances 77 and 78 to the battery feed relay 16 and to ground, respectively. Relay 15 also breaks the circuit of relays 20 and 21 at the back contact of its armature 25; but now, due to a special circuit arrangement, relay 21 is not permitted to deenergize. Since relay 19 is in operated position, when relay 15 pulls up a circuit is closed for relay 22 at the working contact of armature 25. and upon energizing, said relay 22 closes alocking circuit for relay 21 at its armature 48. Relay 21 is slightlyslow acting and this locking circuit is closed before it has time to deenergize, the circuit extending to ground at armature 4.0 when it is first established and then, upon the deenergization of slow acting relay 20, being transferred to the relay and is so line relay 101 completion of the connection but may,

grounded conductor 9 by way of armature 51 of relay 23. An additional result of the energization of relay 22 is the closure of a circuit for the reversing relay 18 at armature 49. Upon energizing, relay 18 reverses the direction of current flow in the conductors of the calling line the same as it did in the connection previously described, except that in the present case, since relay 17 is in operated position, the lower winding of the is not short circuited, and the resistances 81 and 82 are connected in series in the two sides of the line circuit, respectively. ,These resistances, it may be mentioned, are used merely to prevent an unnecessarily heavy flow of current over the toll service trunk.

When the current is reversed in the conductors of the trunk line the polarized supervisory relay which is in bridge of the lineat the operators cord circuit is operated and lights the supervisory lamp. The lighting of the lamp advises called line has become idle and that the connection has been completed. The next operation is to ring the called subscriber. It will bevobserved .that in a case where the toll operator is calling, the automatic ringing does not start immediately upon the however, be started at any time thereafter by the operator. To accomplish this the operator simply has to actuateher ringing key momentarily whereby ringing current is projected out over the trunk line and actuates the alternating current relay 23 at the repeater E, said relay being now connecte around the condenser which connects the two left hand windings of the repeating coil R. Belay 23 is accordingly operated and at the back contact of its armature 51 breaks the locking circuit of the ring-cut oft relay 21, At the same time relay 23 connects ground to conductor 62 in order to insure that line relay 101 will not be caused to de energize, or chatter its armature, by the ringing current, as might otherwise some times occur. When the locking circuit 0 the ring cut-ofi relay 21 is broken this relay falls back and closes the usual ringing circuit. The called station is now signalled automatically in the usual manner. Then the called party answers receiver from the hook the ring out off relay 21 pulls up again and reestablishes its locking circuit at its armature 45, the operator having by this time restored her ringing key and relay 23 being in normal position. The

talking circuit having been completed, relay 16 is energized by flow of current over the called line and upon attracting its armature 29 closes a circuit for relay 24. Upon energizing, relay 2 1 disconnects conductors 72 and 7 3 from conductors 62 and 63, respec tively, and connects the resistance 83 in the operator that the t established by a local and removes his bridge of the two latter conductors, thereby completing a local energizing circuit for the line relay 101 of the selector F Conduc: tors 7 2 and 73are now entirely disconnected from any current. source and it follows that the flow of current over the trunk line commg from .the operators position will entirely cease. As a result, the supervisory relay at the operators cord circuit is denergized and the supervisory lamp is extinguished. By

this means the operator is notified that the called subscriber has answered his telephone, and she may now out in on the line with her listening key and talk to the called party in order to ascertain whether or not he is the party actually wanted. or for any other necessary purpose. WVhen all is ready the required toll connection may be completed by inserting the other end of the cord circuit in use in thejack associated with the toll line over which the-call has been received and the subscribers may converse "as desired.

Attention is called to'the fact that when a toll connection is established as described in the foregoing paragraphs the release of the connection is taken away from the con trol of the toll operator and is controlled bythe called party after he has answered. This is accomplished by the relay 24 which closes a local circuit for the line relay 101 oi. the selector F, and at the same time cuts said line relay oit from the trunk line which comesfrom the operators position. This arrangement of the circuits permits the operator to withdraw the plug from the jack in order to change cord circuits without releasing the connection. And in addition, because of the absence of current flow on the trunk, it produces a quiet and eflicient talking circuit. Although all the relay operations which take place at the connector during the establishment of the foregoing connection have not been gone over in etail, these operations will be readily understood because of the explanation which was "ivcn in the case where the connection was subscriber in the main exchange; and it may be stated at this time that the circuit operations which take lace at the connector H are the same. in all cases regardless of whether the connector is being used in a toll connection or in a local connection. The differentiation between toll and local calls is done at repeater E Calling attendant at branch exchange.

exchangeconnections by local main exchange subscribers and by been explained, it remains now the toll operators having to explain the establishment of certain other classes of connections which may be considered as variations of the above, certain operating features at the attendants and which introduce v cabinet. Inasmuch as all of the equipment in the branch eXchange operates substantially the same no matter whether the calling party is a toll operator or a local subscriber in the main exchange, the various connections which will now be considered will be gone over only once, it being assumed that the calling party is a toll operator; and where any difference exists, or special operations are required, mention will be made thereof in the course of the explanation.

The first connection of this kind which will be explained is where the toll operator calls the attendant at the branch exchange.

It will be understood that although most of the subscribers at the branch exchange may be called directly, their numbers being listed in the general directory, it is impossible to secure all desired connections in this way, as there are always a certain percentage of calls to a private branch exchange which must be directed to the attendant operator and then routed by her to the proper local stations. As a matter of fact, the principal reason for providing an attendant is to have some one who is familiar with the local departments ready to answer calls then necessary, route the calls to the proper stations, and exercise general supervision over the incoming traffic. In order to provide for calling the attendant operator the tenth level of the incoming connectors is reserved, and the circuits are so arranged that when a connector is raised to this level its further operation is prevented and a ring down relay at the attendants position is connected in bridge of the trunk in use in readiness to be operated by ringing current which is automatically transmit-ted over the trunk line, the automatic ringing operation being started immediately when the calling party is a local subscriber in the mainexchange or later on at the option of the operator when the calling party is the toll operator. The circuits will best be understood from a detailed consideration of the operations which take place and this will now be proceeded with. In its preliminary stages the connection is established precisely as has been already described, a toll first selector being 0perated to establish connection with the repeater E,'after which the special second selector F is operated to extend the connection to the connector H. The next digit to be called is the digit 0 and when the calling device is operated in accordance with this digit the connector H is operated under control of the line relay 205 to raise its shaft step by step until the wipers stand opposite the tenth level. On the first vertical step the' circuit of the ring out off relay 210 is closed by the slow acting relay 207, which operates in series with the vertical magnet, and upon energizing relay 210 establishes a locking circuit for itself and. also closes a circuit for the slow acting relay 203, all as previously explained. When the shaft is raised to the tenth level, the tenth level switching springs are shifted and spring 290 is disengaged from spring 289 and is brought into engagement with spring 291. When this occurs a circuit is completed for relays 213 and 209 as follows: grounded conductor 164, armature 255 and its working contact, springs 290 and 291, resting contact of armature 257 and the said armature, and windings of relays 209 and 213 in parallel to battery. Relays 213 and 209 are accordingly energized and the latter relay reverses the heavy line conductors at the connector and also opens the circuit of relay 203, which deenergizes and closes the circuit of relay 206. Upon energizing, relay 206 cuts off the line relay 205. Before this occurs, however, due to the reversal of the line conductors by relay 209, the electropolarized relay 15 at the repeater E is operated with the result that relays 22 and 18 are energized and relay 20 is deenergized, the deenergiza'tion of relay 21 being prevented as previously explained by the establishment of a new locking circuit when relay 22 pulls u Returning to the connector H, the line reTay 205 has been disconnected, as stated, and relay 200 is connected to the lower line conductor in order to hold up the slow acting release relay 204 and prevent the release of the connection. With the switch in this condition the ring down relay 150 at the operators position is bridged across the trunk line as follows: from upper trunk conductor 163 by way of the upper winding of relay 150, conductor 153,.and rotary off normal springs 296 to the upper line wiper 273 which, since relays 213, 210, and 209 are energized, is connected to the lower trunk conductor 154 by Way of armature 266 and its working contact, armature 252 and its working contact, and the working contact of armature 247 and the said armature. The toll operator may now throw her ringing key with the result that ringing current is projected over the trunk line to operate the alternating current relay 23 at the repeater E. This breaks the locking circuit of the ring out off relay 21, which accordingly deenergizes and closes the ringing circuit. The ring down relay'150 which is in bridge of the trunk at the branch exchange is now operated, locks itself at its lower armature, and for the call signal or answering lamp at the attendants position.

lVhen the attendant perceives the lighted lamp she will respond by throwing her key K to listening position. By this operation the locking circuit of relay 150 is broken and the said relay deenergizes and extinguishes the answering lamp. In addition, when the listening key is operated the-lower winding 

